JTM45 Build, how close is Weber's Kit - my JTM30 is gone

[geardoc]

I can't remember if it is the 2nd or 3rd time, but the JTM30 combo ate a power transformer. I don't know why.

I have had good luck with Weber in the past, especially Mike building a kit up there in Indiana.

I'd buy someone's already built but I hear one hell of a difference in tone.

I want to use it with a 2x12 with Celestions. What I really want is just a head.

I've considered asking about Chinese copies, I have this piece of crap called a Bootlegger 30/15 and it was at a pawn shop for $90. I found out it is somewhere between a Fender and Peavey design- more Peavey. It has no tone. I don't know how I would find a Chinese build copy that is a JTM.

Thank you.

 

[fitz]

I can't remember if it is the 2nd or 3rd time, but the JTM30 combo ate a power transformer. I don't know why.

I have had good luck with Weber in the past, especially Mike building a kit up there in Indiana.

I'd buy someone's already built but I hear one hell of a difference in tone.

I want to use it with a 2x12 with Celestions. What I really want is just a head.

I've considered asking about Chinese copies, I have this piece of crap called a Bootlegger 30/15 and it was at a pawn shop for $90. I found out it is somewhere between a Fender and Peavey design- more Peavey. It has no tone. I don't know how I would find a Chinese build copy that is a JTM.

Thank you.

I don't think you're going to get JTM30 tones from a JTM45.
They are very different amps despite the common moniker.

 

[Gunner64]

Weber kit. No. I bought a unused 6m45p kit on Reverb because It was relatively cheap at around $400. Came with tubes and a nice headbox, so it seemed like a deal.

Aside from the headbox, (which was very nice ) they used the cheapest parts they could find throughout. I replaced the pots, the jacks, the wire, and could have kept going replacing the transformers ect.

The Weber kit used a Fender style tag board, not a turret board, and an over complicated giant cap board with 15 or 20 caps on it instead of using simple cans. I ditched the cap board and incorporated cans. So another thing I changed.

Nothing fit in the chassis as per the diagram. I was Pretty disappointed. I feel this whole kit was Not thought out very well.

I won't buy another Weber kit. by the time I was done replacing things I could have bought a much better kit...nice headshell though, I'll give them that.

And as Fitz said the JTM45 and JTM30 are totally different amplifiers, with not much in common other than The JTM branding.

 

[Mike_LA]

FWIW, I built 3 Weber 6G15 kits and had no issues.
Just got a JTM30 myself.
The JTM30s are fairly inexpensive just get another.
From our other thread Gene postulated that many overheating issues were due to proper tubes and screwy speaker taps.

https://www.marshallforum.com/threa...o-amp-30w-1x12-yea-or-nay.132017/post-2366249

Gene Ballzz said:
The ONLY power tubes that should be in there (if amp is stock/unmodified) is the SOVTEK 5881/6L6WGC. These are slightly different than other 5881 & 6L6 tubes and any other tubes will likely have caused heating issues!

The speaker out jacks function in an odd way. The "Extension" speaker jack (for 8 ohm use) only functions if something is also plugged into the "Internal" 16 ohm jack. This means that for 8 ohm operation, you must use either two 16 ohm speakers on separate cables "OR" plug a single 8 ohm speaker out of the "external" jack and plug a dummy (unwired) plug into the "Internal" jack to properly activate the switching. Kinda goofy, but that's the way it is. I suspect that folks not understanding this has been a source/cause for overheating by running an 8 ohm load out of the 16 ohm jack, over the years!

 

[fitz]

The speaker out jacks function in an odd way. The "Extension" speaker jack (for 8 ohm use) only functions if something is also plugged into the "Internal" 16 ohm jack. This means that for 8 ohm operation, you must use either two 16 ohm speakers on separate cables "OR" plug a single 8 ohm speaker out of the "external" jack and plug a dummy (unwired) plug into the "Internal" jack to properly activate the switching. Kinda goofy, but that's the way it is. I suspect that folks not understanding this has been a source/cause for overheating by running an 8 ohm load out of the 16 ohm jack, over the years!

The JTM30 manual is kinda vague about this:

But both the JTM60 & JCM600 manual say you can use a single 8 ohm load in the extension jack.
Makes sense to me with a switching jack on the extension side.
16 ohm pass through the unused extension jack, or disconnect the 16 tap when extension is used, w/ parallel to the main jack to the 8 tap.
Dangling a patch cable out the main for a single 8 ohm load in the extension shouldn't matter.

 

[Gene Ballzz]

@fitz ,
Yes indeed, that blurb from the JTM30 manual is ambiguous at best! I can't guarantee that all JTM30 amps are like this, but the three different ones I've experienced were all the same.

Try this, as an experiment, understanding that we don't want to crank anything or leave the amp on for any lomger than a quick test takes.

Unplug the internal speaker from the INTERNAL jack and plug it out of the EXTERNAL jack. Confirm that you will likely get no sound! Then plug a dummy jack (or un connected cable) into the INTERNAL jack. You will now likely get sound from that EXTERNAL jack. Please understand, that I was not suggesting "dangling" a cable, but instead just using any unwired tip/sleeve plug as the dummy plug, to acuate the switch in the INTERNAL jack. Sure, dangling a cable can work, but it is even less elegant.

I kinda get what Marshall was trying to accomplish here, but it doesn't work well for a single 8 ohm speaker load! The info for the JTM60/600 simply confuses the issue even more!

Just Crankin'
Gene

 

[fitz]

Try this, as an experiment, understanding that we don't want to crank anything or leave the amp on for any lomger than a quick test takes.

Unplug the internal speaker from the INTERNAL jack and plug it out of the EXTERNAL jack. Confirm that you will likely get no sound! Then plug a dummy jack (or un connected cable) into the INTERNAL jack. You will now likely get sound from that EXTERNAL jack.

Running the bottom cab from the Ceriatone - H-30(55) 8 ohm into the extension jack.
Sounds fantastic, btw.
Wouldn't want to crank the amp through the greenback, but I've also run a H-75 8 ohm in the combo this way.
And I've run the 600 to an 8 ohm 1965 from the extension jack on that amp.

 

[Gene Ballzz]

Running the bottom cab from the Ceriatone - H-30(55) 8 ohm into the extension jack.
Sounds fantastic, btw.
Wouldn't want to crank the amp through the greenback, but I've also run a H-75 8 ohm in the combo this way.
And I've run the 600 to an 8 ohm 1965 from the extension jack on that amp.
View attachment 132157

Well Sir,

It appears that yours is wired more logically! It would be interesting to know the manufacture date, as possibly the issue got corrected, over the rather short run of production? Its funny that the early (poorly detailed) schematics show the goofy wiring, but all of the current "re-draws" seem to show the goofiness corrected!

Enjoy,
Gene

 

[Mike_LA]

I also just ran the test and got the same result as @fitz
Plugged the cab speaker into the extension jack only and still have sound.

 

[fitz]

Well Sir,

It appears that yours is wired more logically! It would be interesting to know the manufacture date, as possibly the issue got corrected, over the rather short run of production? Its funny that the early (poorly detailed) schematics show the goofy wiring, but all of the current "re-draws" seem to show the goofiness corrected!

Enjoy,
Gene

The 30 is a '95 & the 600 is a '97.

I've had the boards out of both to correct other issues, but never actually visually confirmed my switching jack theory, but it seems logical, and functionality of the units I have seem to confirm my suspicions.

It would be much less confusing if Marshall just labeled the jacks 16 ohm on one, 8 ohm on the other, and 2x16 with both - at least that's how mine seem to function.

I think they just assumed that we're all complete idiots, and would only ever use the recommended internal & external genuine Marshall products.
Little did they know, we're even bigger idiots, and try every possible combination of whatever gear we have.

 

[Central Scrutinizer]

https://www.tubesandmore.com/sites/default/files/uc_products/p-t290qx_oct2018_main1.png

New Hammond transformer $146

Transformer brands elicit as many naysayers as brands of motor oil (Valvoline and Mobil 1 are the best).

But if it keeps a favorite amp working why not at least check it out?

 

[geardoc]

I cannot justify the instability in the amp. I have had it since nearly new, it was a demo amp for the JTM30 and JTM60. It came with Sovtek's and I have not used up the ones I was given with it, they gave me 6 of each tube because they were trying to push Sovtek pretty hard, pedals, . Strange Days. I have the original manual.

The music store I bought it from was in Athens GA, I guess this was early-mid 90s. They carried the JTM45 which was expensive enough that at that date I would never have been able to afford it. They were also pushing E-H Sovtek MiG and then Red Bear and later Matamp assembled Orange so called Reissues, and Trace Elliot assembled Orange (bass) so-called Reissues.

I keep a pretty detailed ledger of gear for insurance purposes. If I were to replace it, this would be the 4th transformer overall I am aware of.

I want to find a JTM45 kit head and just go with that. I have enough cabinets that I would prefer a head. I almost bought that Fuzzlord FTW45 but other than the FTW name plate I was not aware of anything that made it worth $2k

I may have to take the kit road. Bummer.